The present invention relates generally to circuitry and methods for powering a light source such as an LED load. More particularly, the present invention relates to methods for dynamic adjustment of power parameters for LED drivers.
Light emitting diode (“LED”) lighting is growing in popularity due to decreasing costs and long life compared to incandescent lighting and fluorescent lighting. LED lighting can also be dimmed without impairing the useful life of the LED light source.
LED loads are DC current driven, so a DC-DC or AC-DC converter is needed to regulate the current going through the LED in order to control the output power and luminance. An exemplary dimmable LED driver 10 is represented in FIG. 1. As shown, a typical four-wire output 0-10 v controllable AC-DC converter 14 is positioned between the AC mains input 12 and the LED load 16. This AC-DC converter regulates the DC current going through the LED lighting module and also receives control signals from dimming control block 18 in order to set the output current dynamically. Typically, a DC voltage 20 is provided as the input of the dimming control block 18. The dimming control block will sense the voltage level 20 (e.g., V_control) and set the control signal 22 for the reference of LED output current according to a preset relationship between the two values 20, 22.
The output range of the LED driver as shown in FIG. 1 typically is limited with values for a maximum output voltage (Vout_max) and maximum output current (I_out_max) as are associated with a maximum output power for the particular LED driver design, which means that there is only one maximum output current and one maximum voltage for this driver in steady state operation.
An exemplary operating range for this type of LED driver is shown in FIG. 2, wherein the operating area is limited to the highlighted region as further defined by a maximum current (I_max), minimum current (I_min) and maximum voltage (Vmax). When the output current changes the maximum output voltage would remain the same.